1. Field of the Invention
The present invention relates to aromatic polyazomethines. In particular, it relates to aromatic polyazomethines containing trifluoromethylbenzene units in the polymer backbone structure.
2. Description of the Related Art
Aromatic polyazomethines or polyimines have been classified as highly conjugated low molecular weight materials which are generally insoluble and intractable. The insolubility of these polymers makes solution synthesis difficult. Melt polymerization techniques have resulted in infusible materials which cannot be further fabricated into thin films or remolded.
Early attempts to synthesize polyazomethines or polyimines involved the condensation reactions of dialdehydes with various aryl diamines in several solvents. This resulted in the formation of yellow-to-orange insoluble, infusible brickdust products of low molecular weights which ranged from 500 to 1000 g/mol. The low molecular weights were attributed to the insolubility of the condensation products which separated rapidly from the solvent media causing the polymerization to stop before high molecular weights could be obtained. In order to increase the molecular weights of the products, solvents were changed, catalysts were added, the reaction temperature was varied and dehydrating agents were used, none of which resulted in a significant improvement in the molecular weight. The degree of polymerization ranged from 3.4 to 8.0, as calculated by nitrogen analysis, for these aromatic polyazomethines. The early work, chemistry and properties of various aromatic polyazomethines is reviewed by G. F. D'Alelio (G. F. D'Alelio, Encyclopedia of Polymer Science and Engineering, Vol. 10, 1st Edition, John Wiley and Sons, New York, 1969, p. 659) and G. F. D'Alelio et al. (G. F. D'Alelio, J. V Crivello, R. K. Shoeing, and T. F. Huemmer, Journal of Macromolecular Science and Chemical Education, A1 (7), 1161, (1967)).
In order to synthesize high molecular weight polyazomethines, D'Alelio et al. used melt polymerization techniques and bis-exchange reactions. The polymers which resulted from these synthetic approaches yielded shiny black, infusible materials. They were sparingly soluble in dimethylformamide and completely soluble in sulfuric acid. However, sulfuric acid degraded the polyazomethines causing them to become a dark color in solution and form the amine-salt ions which caused the intrinsic viscosities to increase with time.
Despite several undesirable physical properties displayed by polyazomethines, it was hypothesized that these rigid polymers might display thermotropic behavior if their melting points could be decreased below their decomposition temperature. Morgan et al. (P. W. Morgan, S. L. Kwolek, and T. C. Pletcher, Macromolecules, 20,729, (1987) and P. W. Morgan U.S. Pat. Nos. 4,048,148 and 4,122,070), synthesized a series of polyazomethines which incorporated toluene, chlorobenzene, anisole, ethane and 1,2-dioxyethane units into the polymer backbone. These polymers were synthesized both in the melt and in solution using a variety of techniques, however, the polymer precipitated in each case. The resulting polyazomethines were then heated to a temperature above their melting point where they displayed thermotropic behavior in the melt and were able to be melt spun as fibers or compression molded into films and bars. The inherent viscosities of these polymers were measured in a 98% sulfuric acid solution and ranged from 0.4 to 2.0 dL/g for the gelled solution polymerization products, and up to 6.0 dL/g for the melt spun fibers. No data was given for the film properties.
Wojtkowski (P. W. Wojtkowski, Macromolecules, 20, 740, (1987) and Harris et al. (F. W. Harris and K. Sridhar, Polymer Preprints, 29 (2), 304, (1988)) also inserted aliphatic units and substituted benzene rings into the polymer backbone in order to generate polyazomethines which displayed melt anisotropy. When these polymers were heated above their melting points, some of them could be melt spun as organic fibers. However, these thermotropic polyazomethines were only soluble in strong acids, hot protic solvents and salt solutions which severely limited any possibility of solution processing.
Imai et al. (Y. Imai, N. N. Maldar, and M. Kakimoto, Journal of Polymer Science, Polymer Chemistry Edition, 22, 3771, (1984)) used aryl diamines with large pendant aromatic fused ring structures to synthesize soluble polyazomethines. One series of soluble polyazomethine copolymers were synthesized by condensing various ratios of isophthalaldehyde (IPAd) and terephthalaldehyde (TPAd), with 4,4'-oxydianiline (ODA) and 2,5-bis(4-aminophenyl)-3,4-diphenylthiophene (TPTDA) in N-methylpyrrolidinone (NMP). The resulting copolymers had inherent viscosities ranging from 0.45 to 0.84 dL/g depending on either the IPAd/TPAd or the ODA/TPTDA ratio. However, the polyazomethine copolymers which contained less than 40% IPAd in the IPAd/TPAd ratio when condensed with TPTDA were insoluble in NMP, as were the polyazomethine copolymers containing only IPAd and greater than 50% ODA in the ODA/TPTDA ratio.
Another series of polymers was made by Mohite et al. (S. S. Mohite and P. P. Wadgaonkar, Polymer Preprints, 31 (1), 482, (1990)) who condensed IPAd or TPAd with 9,9-bis(4-aminophenyl)fluorene or hexamethylene based diamine in m-cresol. Copoly(azomethine-ester)s containing 6F-isopropylidine units were also made. Both of these types of polymers were soluble in a variety of solvents, but the resulting inherent viscosities were below 0.3 dL/g and the cast films were very brittle and of little consequence.
The polyazomethines which have been synthesized thus far have only been useful as organic fibers. Generally, these polymers are highly conjugated and intractable. Those which display some solubility either have not demonstrated any mechanical integrity or are soluble in solvent systems which are detrimental for solution processing into films, matrix resins for composites, or adhesives and coatings.
An object of the present invention is to prepare soluble, amorphous, aromatic polyazomethines which contain trifluoromethylbenzene units.
Another object is to prepare polyazomethines which remain isotropic after thermal treatment.
Another object is to prepare films, adhesives, composites, and coatings from these soluble polyazomethines.